1. Field of the Invention
This invention relates to a method of manufacturing a mask, such as a photomask, a phase-shifting mask, etc.
2. Description of the Related Art
The process of manufacturing a semiconductor device involves a pattern-forming step or so-called lithography step for forming various kinds of patterns on a semiconductor wafer. In this lithography step, a mask, such as a photomask, a phase-shifting mask, etc. is employed.
In recent years, to meet the trend to further refine or miniaturize a semiconductor device, an increasingly severe dimensional accuracy is now required for the mask of this kind. For example, the dimensional uniformity in-plane (in-plane uniformity) of mask is now required not to exceed over 10 nm.
According to the conventional manufacturing method of a photomask, a mask pattern is formed on a mask blank on the basis of specifications at first, and then, it is determined whether or not the mask is non-defective or defective. There are a large number of judgment items, and if any one of these judgment items fails to meet a specified condition, the mask is deemed as defective.
For example, in the case of a half-tone type phase-shifting mask, there are 11 items as representative specification items and specification values involved therein as shown in FIG. 1. If a mask fails to satisfy any one of these specification values among these items, the mask is deemed to be defective according to conventional practice. Therefore, in spite of the recent developments in enhancing the fineness in the mask manufacturing technique, the yield of the mask is very low.
A method of manufacturing a photomask according to an aspect of the present invention comprises determining an average value of dimensions of a pattern in a photomask, determining an in-plane uniformity of the dimensions, determining an exposure latitude on the basis of the average value and the in-plane uniformity, and judging if the photomask is defective or non-defective on the basis of whether or not the exposure latitude falls within a prescribed exposure latitude.